Schottky diodes are very well known and normally employ a high work function material which is in contact with an epitaxially grown N silicon surface. The Schottky diode has the advantage over a P/N junction diode of very high speed reverse recovery, permitting their use in very high frequency applications. Higher voltage prior art Schottky diodes frequently employ a P.sup.+ guard ring diffusion which encloses and contacts the contact metal. Such prior art devices, and a process for their manufacture, are typically shown in U.S. Pat. No. 4,899,199 to Herbert Gould. The guard ring, at lower voltage, causes low leakage current and a very sharp avalanche breakdown characteristic.
Presently known Schottky diodes are usually rated at less than about 200 volts. However, as the reverse voltage increases, a higher resistivity epitaxial silicon is needed. Thus, the forward current can cause a resistive voltage drop in the epitaxial silicon higher than a diode drop (about 0.7 volts). This then causes the N.sup.- /P.sup.+ junction to be forward biased to inject minority carriers during forward conduction. The main advantage of high speed turn-off is then lost.